Adding an IO Data and keyed service to previews/

chrome/browser/previews/previews_service.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/previews/previews_service.h"
+
+#include "components/previews/previews_ui_service.h"
+#include "content/public/browser/browser_thread.h"
+
+PreviewsService::PreviewsService() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+}
+
+PreviewsService::~PreviewsService() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+}
+
+void PreviewsService::set_previews_ui_service(
+    std::unique_ptr<previews::PreviewsUIService> previews_ui_service) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  previews_ui_service_ = std::move(previews_ui_service);
+}